Motion estimation in general, and global motion estimation in particular, is a common field of activity within video processing. Global motion estimation usually serves as an enabling technology to a wide variety of algorithms, such as temporal interpolation and camera stabilization. Global motion estimation is sometimes used as a cost-effective alternative to block/pixel accurate motion estimation.
A fundamental problem in global motion estimation is to distinguish between global and non-global motion. Global motion estimation assumes that all motion in an image can be summarized in a few parameters. When the assumption of global motion estimation does not hold, then a global motion estimation will come up with unreliable answers, as it is designed to come up with a simple answer, one that does not explain, say, a globally moving scene with one or more independently moving objects in it.
Problems that are not yet satisfactorily solved relate to whether global motion estimation can be used to reliably find background motion in the presence of foreground objects, whether global motion estimation can be used to estimate the motion of the foreground objects, and how to know when the motion is global.